Not yet complete but already being hailed as a model of design efficiency, the Blennerhassett Bridge connecting West Virginia to Ohio is expected to improve access to major cities east and west of the Ohio River, and greatly enhance the economic development of the region.
A joint venture between the Ohio Department of Transportation (ODOT) and the West Virginia Division of Highways (DOH), the bridge will complete the upgrading and widening of U.S. Highway 50 from Clarksburg, W.Va., to the Ohio state line. A project more than 40 years in the making, U.S. 50 is one of the original 23 Appalachian corridors selected under the Appalachian Development Act of 1965.
But being the final link to U.S. 50’s completion won’t be the bridge’s only claim to fame. Once it opens, the span will take its place in the record books, not once but three times:
Engineering challenges But before earning such impressive accolades, equally impressive challenges needed to be overcome. These challenges stemmed from the bridge’s namesake, Blennerhassett Island, in the Ohio River. The island is a historic state park, and bridging it presented several obstacles, including the sensitive issue of wetland mitigation. But it was the island’s past that drew most of the attention and public involvement. Archaeological excavations unveiled traces of settlements dating as far back as 9,000 years ago. And in 1798, Irish immigrant Harman Blennerhassett built a 7,000-square-foot mansion on the island, considered to be one of the most elegant estates in West Virginia. The mansion was so valued by West Virginians that when it was destroyed by fire in 1811, the state recreated the Palladian-style home on the island’s upper end.
Given the island’s sensitivity, ODOT and the DOH consulted at great length with architectural, environmental and historical stakeholders about the type of bridge that would best preserve and blend with its natural and historic surrounding. The meetings produced a strict list of requirements. There were to be no piers on the island and the span itself was to be low-profile as to not interfere with the view from the mansion. Both criteria presented prime design consultant Michael Baker Corp., and major subconsultant HNTB Corporation with a formidable challenge.
The design team collaborated and returned with the recommendation of a suspension bridge. By the final design stage, however, estimated costs were nearing $135 million and increasing. The suspension design had met the rigid criteria but had significantly exceeded the budget, putting the bridge’s future in jeopardy. As a result, the DOH went back to stakeholders and asked them to reconsider construction on the island. The stakeholders acquiesced and ensuing studies confirmed the tied-arch option would be more cost-effective. A second environmental evaluation was conducted based on island construction and designers huddled up again to develop a new concept.
In 2003, nearly four years after first meeting with stakeholders, the DOH approved a tied-arch design. Anchored by three carefully located piers on the inland, the Blennerhassett Bridge is composed of three sections:
The tied-arch design ultimately would save the project between $45 million to $50 million. With West Virginia agreeing to pay $16 million, Ohio contributing $8.4 million and the remainder to be paid with federal funding, the final link of U.S. 50 began to take shape. Rising out of the river bottom, the bridge rests on two abutments and 11 piers, 10 of which are founded on caissons varying in width from 54 inches to 108 inches. The caissons were drilled with polymer slurry at the bottom to help stabilize the sandy/silty soils.
Tied-arch design The Blennerhassett Bridge’s tied-arch design has been compared to a drawn bow, with the bridge deck representing the string and the steel arch, the bow’s handle. Unlike most arch bridge designs, which place the deck on top of the arch, the Blennerhassett Bridge deck rests below the arch. The network of cables supporting the roadway forms a redundant load path, precluding the need for visually massive fortification. At the same time, crossing the cables stiffens the structure, creating the bridge’s sleek, 175-foot-high signature arch, which blends with the surrounding landscape.
The bridge deck is 100 feet wide, accommodating four, 12-foot lanes with two, six-foot shoulders in each direction separated by a median barrier. Using the shoulders for traffic, the bridge can expand to six lanes if needed in the future. Because of the bridge’s width, both the deck and rib bracing systems are box-shaped in cross section to enhance redundancy. The four plates that compose the cross section are bolted together along the corners, preventing a fracture from spreading to adjacent plates.
The tied-arch design also enlisted the second edition of the Load and Resistance Factor Design specifications from the American Association of State Highway and Transportation Officials for design criteria, which helped the project meet its budget and provide uniform safety levels, ensuring superior serviceability and long-term maintainability.
Inclined hanger network The bridge design also employs a network of inclined steel hangers, which acts like a truss. The inclined hangar system is said to be 10 times stiffer than a vertical hanger system, while using exactly the same material quantities. Saving about two million pounds of steel, the network substantially reduces live load deflections and bending moments in arch ribs and tie beams.
The hangers are based on cable-stay technology. Each cable consists of a bundle of 27 individually lubricated and sheathed wire strands enclosed by a high-density polyethylene duct. While widely used for cable-stayed bridges, this application is a first for an arch bridge in the United States.
The hanger system also provides triple corrosion protection. Additionally, strands are individually attached to an anchor head. This concept permits installation and replacement of one strand at a time using relatively light stressing equipment. Hanger anchors reside inside the tie girder and arch rib, providing protection from the environment and sabotage and allowing inspections to be performed without extensive rigging.
Steel content The DOH made an executive decision to use hybrid steel plate girders composed of grade 50W and HPS 70W weathering steel because it gave engineers a viable option for the long approaches necessary in the bridge’s design, promised a life span of up to 75 years, and meant fewer piers and less impact to Blennerhassett Island. To mitigate the escalating cost of steel, the DOH, for the first time in its history, purchased the material in its raw form. The agency paid the contractor upfront instead of after fabrication and erection, saving the state from unnecessary financial risk if prices continued to soar.
Today, the bridge has 30 million pounds of high-performance steel with 12 million pounds in the tied arch itself. The West Virginia approach is a continuous girder bridge of eight spans, ranging from 200 to 400 feet and using 8,150 tons of plate girder steel. The Ohio approach has three spans, ranging from 140 to 179 feet and uses nearly 800 tons of steel.
Greater economic development As the final link of U.S. 50, the Blennerhassett Bridge will be a missing link for the area’s economy. The primary objective of the U.S. 50 upgrade is to stimulate economic development. With the Blennerhassett Bridge nearly complete, that goal soon may be a reality.
Photo credits: ©Mike McPheeters 2008, courtesy HNTB
Duane Keener is project manager for HNTB Corporation. Contact him at (304) 292-6411 or dkeener@hntb.com.
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